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Winter winds vs Summer winds (r they stronger)

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Created by nugs > 9 months ago, 24 Aug 2012
Intheozone
WA, 247 posts
28 Aug 2012 9:33AM
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Kitepower Australia said...

beefarmer said...

yet somehow, when you stand on the beach in bali, and you feel a good 25 kt wind in your face, and you look out and see the white caps a good 25 kt wind would produce, you rig up and go out and its not 25 kts, it's 18.

Or at least that's how it seemed to me.





Reckon thats more to do with local issues like depth of water, sun angles, and you being less familiar with wind in Bali - meaning you just under estimated the wind.
16 degrees of temp difference of the air can only make around 1 knot of difference (if that), not 7/8 knots like you are thinking.
Its got to be just underestimating.




Have you even been to far north queensland or Perth to kite??? Compare FNQ with Sydney Wind. what size kites are you riding and what wind speed in each??

Intheozone
WA, 247 posts
28 Aug 2012 9:51AM
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I don't have the time to get the Maths and physics out however I think alot has todo with Humidity. Hot and Humid (think Darwin Cairns Bali) 25kts and I'm on my 12m verses Cold and Dry (Think Perth and most seabreezes) 25kts and I'm flying on my 9m. I don't care what the science says I know that my kite feels a difference

stamp
QLD, 2800 posts
28 Aug 2012 11:57AM
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^^^ i agree, i neither know nor care what the reason is but warmer tropical wind has less grunt.

whatthe
WA, 186 posts
28 Aug 2012 11:59AM
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Intheozone said...

I don't have the time to get the Maths and physics out however I think alot has todo with Humidity. Hot and Humid (think Darwin Cairns Bali) 25kts and I'm on my 12m verses Cold and Dry (Think Perth and most seabreezes) 25kts and I'm flying on my 9m. I don't care what the science says I know that my kite feels a difference


The force on the kite is directly proportional to 0.5*rho*Velocity^2. This is undisputable scientific fact and if we don't believe this, then planes will start to fall out of the sky :)

Plummet has shown that rho (air density) will vary by (at the extreme) 10-15%.

However a wind gust can typically be around 40% stronger than the steady breeze. When you take a steady velocity of 18 knots, this is a gust of 25 knots. So using the Velocity^2, you will see a force change of 92%!!!!

To get a 15% increase in force, you only need a gust of 19.5 knots above the steady 18 knots. (19.5^2/18^2=1.17).

Small changes in velocity will greatly outweigh the effect of density changes. A warm tropical breeze may be more steady at 18 knots, whilst a winter breeze or seabreeze will be more turbulent and gusty at 18 to 25. This is because the winter front(high gradient) or sea breeze (thermal) are shorter in duration (~8 hours) whereas a tropical (low gradient) breeze may be a longer duration (24 hours).

Intheozone
WA, 247 posts
28 Aug 2012 1:07PM
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What the...

Seriously What the #@$%

a seabreeze is one of the most consistant winds you can get.

28 Aug 2012 3:07PM
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Intheozone said...

Kitepower Australia said...

beefarmer said...

yet somehow, when you stand on the beach in bali, and you feel a good 25 kt wind in your face, and you look out and see the white caps a good 25 kt wind would produce, you rig up and go out and its not 25 kts, it's 18.

Or at least that's how it seemed to me.





Reckon thats more to do with local issues like depth of water, sun angles, and you being less familiar with wind in Bali - meaning you just under estimated the wind.
16 degrees of temp difference of the air can only make around 1 knot of difference (if that), not 7/8 knots like you are thinking.
Its got to be just underestimating.




Have you even been to far north queensland or Perth to kite??? Compare FNQ with Sydney Wind. what size kites are you riding and what wind speed in each??


Yep been kiting all over Oz, and even just recently in say Port Douglas it blew approx 24-28 knots, I used a 9M C4 and was well powered up, my friend who is at least 10-15kg heavier than me used a 10.5 Core.
If I was in Perth in similar strength winds, I would be using the same kite, and have used the same size kite in 25 knots at Safety Bay last summer.

whatthe
WA, 186 posts
28 Aug 2012 1:33PM
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Intheozone said...

What the...

Seriously What the #@$%

a seabreeze is one of the most consistant winds you can get.


Based on what exactly? It comes in the same time and direction every afternoon? That doesn't determine how steady (or smooth) the flow itself is. A seabreeze only exists vertically in the bottom so many kilometres above sea level. It is driven by varying heat sources. It swings through a large angle (due to Coriolis effect) during its existence. It only has about 3-4 hours to establish a steady flow and then dies off after around 6 hours.

All these factors can contribute to the turbulence of that flow which will likely change its gustiness. A winter front is even worse.

A seabreeze consistant? Yes. But smooth flowing, I'm not sure.

The maths shows that velocity is the determining factor on kite force. So really, it all depends on the correlation between your perceived wind speed and the actual flow velocity the kite sees at 20m above sea level.

DaGodfather
SA, 280 posts
28 Aug 2012 4:33PM
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I made all the calculations a couple of years ago. I don't remember the exact details any more, but the difference between a typical winter day (10 deg C, wet, frontal weather) and a typical summer day (30-35 deg C, dry, seabrezee) worked out to be around 5%.

The effect of the cold air in winter is PARTIALLY CANCELLED OUT by lower pressure and higher humidity.

Now regarding tropics like Bali etc. - it is true the wind is considerably weaker, because unlike in the South all the factors reinforce each other ie:
- reasonably high temp (say minus 5% density)
- low pressure (say another minus 5% density or more)
- high humidity (say another minus 2% density)

beefarmer
WA, 328 posts
28 Aug 2012 5:33PM
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It seems we are getting somewhere... thanks Al Pacino.

I thought it might be a combination of small factors, humidity/pressure/temp but couldn't think of a quick way to work out what they'd actually have been while I was in Bali

also whatthe's explanation about significant power increases from small gusts probably is part of it too, one thing i would say about the bali wind is it was very consistent, even more so than seabreezes in WA . One problem i was having in the lighter bali winds was working upwind so slowly, over here i tend to make the most of the gusts trying to shoot upwind as much as possible when they come through, i guess i wouldn't have been able to do that as often or as effectively over there - was a while ago now so i don't really remember this but it sounds about right

Plummet
4862 posts
28 Aug 2012 6:18PM
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Well maths aside. My practical experience between winter and summer is this. My temps are lower than you perth guys. We might see maybe 30 as push. but could be down to 5-10 deg c in winter.

Summer seabreases are definately cleaner smoother more predictable. it makes them easier to ride. the winter frontal wind is definately more variable. an 18 knot day is more likely to be a 16-22 knot day.

i ride the same size kites from summer to winter. i don't ride a bigger size for the same wind speed in summer. But i do notice more power in winter on my biggest size kite. that would be the 15m speed 3. i find i have a couple of knots extra low end in the wind which makes the difference between the walk of shame and staying upwind. at the upper end 30+ knots i can't notice any difference. a storm is a storm winter or summer.

Puetz
NT, 2186 posts
29 Aug 2012 11:30AM
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... there is no contest, Darwin is the skinny wind capital of Australia.

I can use my 18/17m kites in upto 30 knots and still have fun, yet in Gerro or a good Perth seabreeze, I'm well lit on my 12m.

Tropics have skinny (read guttless) winds dispite what the anemometer says.

cheers,

Robbie

TurtleHunter
WA, 1675 posts
29 Aug 2012 7:22PM
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^lol I figured you would have a certain knowlage of this subject puetz.
Could skinny winds be caused by non linear wind



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